Air bags where deployed, do I need to replace the air bag sensors?

[Naim]

Wife smacked the front of the car good enough to deploy the air bags.
(Bumper will need to be replaced along with the piece between the headlights.)

I was able to purchase replacements (air bags/computer/a reel) off of ebay for $125.
Then someone mentioned that I will need to replace the sensors located in the fenders because once they have been tripped, they are useless.
True?

Where is a good place to get replacement sensors are a decent price?